Function increase_archlinux_backoff 

pub fn increase_archlinux_backoff(retry_after_seconds: Option<u64>)

What: Increase backoff delay for archlinux.org after a failure or rate limit.

Inputs:

• retry_after_seconds: Optional retry-after value from server (in seconds).

Output: None

Details:

• If retry_after_seconds is provided, uses that value (capped at maximum).
• Otherwise, doubles the current backoff delay (exponential backoff).
• Caps backoff at maximum delay (60 seconds).
• Increments consecutive failure counter.